rational, rationale

Rational or rational means logical or sensible--
When he hit his head he was ranting, but he seems rational now.
Make sure the decision is rational, and not based on emotion.

Rationale or rationale means the set of reasons that account for a decision or for behavior--
His rationale for leaving was that the company would be better off without him, and he owns some of the stock, so he would profit by quitting his own job.
He has promised to explain the rationale that led to his decision.

Now that you know that, you can say--
"She claims it was a rational choice, but her rationale seems to be a sequence of revenge and gloating."

Note--"rationally" describes something done in a logical or sensible way--
He behaved rationally, so it was easy to predict his movements.